The recent reservoir failure that flooded several towns in Hungary with toxic red mud is the latest environmental insult to Europe's Danube River. But it is not the first, nor the worst, disaster of its kind, experts say. (See photos of the mud spill.)

And unless steps are taken to safeguard similar industrial plants and mining facilities around the world, these kinds of accidents will continue to happen, they warn.

On October 4, a so-called tailing dam that held waste products, including arsenic and mercury, from the Ajkai Timfoldgyar aluminum-processing plant in the town of Ajka, Hungary, collapsed. This released an estimated 184 million gallons (697 million liters) of highly alkaline red mud into the Marcal River and nearby towns, killing at least eight people. The toxic flood reached the Danube River—Europe’s second-largest river—last Thursday, sparking fears of downstream contamination.

The Degraded Danube

Hungary Prime Minister Viktor Orban called the spill the country's biggest ecological disaster. But other government officials say there has been no serious impact on the Danube's wildlife because the sludge's toxic substances have been safely diluted by the river—a claim that Greenpeace and other environmental groups have been quick to question.

"To say it's not creating any environmental impact at all would be misleading, but whether those impacts are devastating, it doesn't appear that they are," said Jim Kuipers, a mining-engineering consultant based in Butte, Montana.

The Hungary spill is the latest in a long list of environmental problems affecting the Danube River, including pollution from cities and industry and pesticides and chemical runoff from farms.

"It's sort of like having a bad backache and then having your kid jumping on you," said Emily Stanley, a freshwater scientist at the University of Wisconsin, Madison. "It's an acute injury to a chronically stressed system."

One of the biggest threats facing the Danube today is human alterations to the river made for navigation purposes, according to a 2004 European Commission report. Projects to deepen, dam, or straighten the river and remove "bottlenecks" to vessel passage are changing the river's traditional floodplain landscape and water flow into deltas, as well as destroying wetlands and other protected habitats, according to the environmental nonprofit WWF.

There are currently projects underway to restore the Danube's floodplains, and a recent plan by the International Commission for the Protection of the Danube River (ICPDR) aims to halt the illegal dumping of hazardous materials into the river.

Making Mining Safer?

The total discharge from the dam failure in Hungary is nearly equal to the 200 million gallons (750 million liters) of oil spewed into the Gulf of Mexico from the leaking BP oil well this year. But comparing the two disasters is neither fair nor accurate, Kuipers said.

"The immediate devastation of this dam failure is in a relatively small area, and we haven't seen huge widespread ecological impacts from it," he said.

"But in the Gulf, the widespread impacts are pretty much indisputable, and it's going to cost tens of billions of dollars to clean up. It's not going to cost tens of billions of dollars to deal with the ecological impact of this spill."

But even if the environmental costs from the tailing-dam spill are still unclear, the toll in human life is already too high, Kuipers said.

"If only one person is killed, it's one person too many," he added. "It points to very lax [dam-building] standards in the country as a whole."

Hungary is not unique in this regard, however, said the University of Wisconsin’s Stanley.

“In Eastern Europe in particular, there are a lot of these dams and facilities that are not receiving any kind of oversight any more," she said. "The money is short and the government has just walked away."

Some experts estimate that the rate of tailing-dam failures worldwide is nearly ten times higher than that of typical water dams—and with many of those dams located near rivers and streams, the potential for environmental damage to waterways is high.

For example, if the Akja aluminum plant tailings contained cyanide instead of less toxic arsenic and mercury, the impact on wildlife could have been much worse.

In 2000, just such a spill occurred in Romania when a tailing dam from a gold mine burst, spilling cyanide-laced water into the Tisza and Danube rivers and killing up to 80 percent of aquatic life along some stretches.

Scientists and environmental groups worry that as mining projects grow larger, the tailing dams built to serve them will pose increasingly larger threats should they fail.

For example, a tailing dam proposed for the headwaters of Bristol Bay, Alaska, would be among the largest dam of any kind in the world. If that dam were to break, "the scale of what happened in Hungary will seem like child's play," said Alan Septoff, research director of Earthworks, a nonprofit environmental group based in Washington, D.C.

Another concern is the large number old tailing-dams that are aging without proper maintenance or repair.

"Dams are like baby boomers," the University of Wisconsin's Stanley said. "They get old, they age, and they begin to show signs of deterioration. Without inspection and regular repairs and maintenance, I think it's highly likely that we'll see more of these [failures] in the future."

Fortunately, the mining industry has demonstrated that it’s capable of change, she said. The bad news is that it has sometimes required a catastrophe to do so. For example, in 2008, a tailing dam rupture at the TVA Kingston Fossil Plant in Tennessee released more than 1.1 billion gallons (6.8 billion gallons) of coal fly ash flurry—a byproduct of coal combustion—into the Emory River.

"As a result, the U.S. Environmental Protection Agency and others immediately undertook an evaluation of all similar facilities in the United States," Kuipers said.

"In the same way, the [Hungary spill] is a call for similar facilities throughout the world to undergo inspection and change their operational situation to prevent this type of event from occurring."

Stanley is similarly hopeful. "Maybe this is a difficult thing for Hungary, but a wake-up call or the rest of the world about managing these wastes," she said.